Radio receiving set



p 1938. D. H. MITCHELL 2,130,243

RADIO RECEIVING SET Filed Aug. 12, 1935 Patented Sept. 13, 1938 UNITEDSTATES RADIO RECEIVING SET Donald H. Mitchell, Chicago, Ill., assignorto Galvin Manufacturing Corporation, Chicago,

111., a corporation of Application August 12,

1 Claim.

This invention relates to radio chassis and especially to shielding andstructural features thereof. The invention relates particularly to aradio chassis for use in automobiles and the like, where 5 there arespecial problems of compactness and shielding.

Although the need for shields around various parts of radio sets haslong been recognized, the problem of providing adequate shielding at aminimum cost and in a minimum space has remained vexatious. It wasparticularly hard to secure adequate shielding around a vibratinginterrupter such as is used in producing high voltage B current from astorage battery as in automobile radios. In automobile radios thisproblem is aggravated by the need for extreme compactness which placesthe interrupter very close to other parts of the radio system whichwould be affected by even very weak interference from the interrupter.

The problem with respect to the interrupter has been solved by providinga light weight container and magnetic shield for the interrupter incombination with a cast base provided with lugs for screwing it firmlyagainst the frame of the chassis and interposing a resilient contactmember between the chassis frame and the base. This resilient contactmember makes contact with both the base and the chasis frame at aplurality of points. The combination of these features provides anextremely low resistance shield structure at a very low cost.

Another form of shield which is of especial value in connection withparts of the set which need not be magnetically shielded, is theprovision of a tubular shield having a threaded screw receiving holeformed thereon by punching straps out of the plane of the Wall of theshield with punching dies which have threads formed thereon wherebythreads are formed on the punched straps.

Other features and advantages of my invention will be apparent from thefollowing description taken with the drawing, in which:

Fig. 1 is a view mainly in elevation of a radio chassis carrying thereonthe shield of my invention and illustrating further, in section, aportion of the housing for the chassis.

Fig. 2 is a fragmentary detail illustration in perspective of one formof shield shown in Fig. 1 assembled on a chassis.

Although this invention may take numerous forms, only one chassis hasbeen chosen for the purpose of illustration. The chassis includes achassis frame II on which various parts of the receiving set aremounted. One of the parts Illinois 1935, Serial No. 35,704

which has given the most trouble from the standpoint of shielding is thevibrating interrupter l2 which includes an electromagnet operating oneor more pairs of make and break contacts. These interrupters haveheretofore been provided with shields I3 formed of sheet iron usuallytin-plated. This shield in formation and material resembles an ordinarytin can.

In the past this shield has proved inadequate, but I have found that itcan be made quite satisfactory by combining with it a thick base I6which telescopes over the end of the shield I3. This base I6 ispreferably cast of die metal and may be secured to the shield I3, in anysuitable manner. Although the drawing shows little difference inthickness between the base I6 and the shield I3, it should be understoodthat as a matter of fact the base I6 would be several times as thick asthe ordinary sheet metal used in such shields. The base I6 may haveprovided thereon integral lugs I8 through which bolts 20 may extend toand engage the chassis frame II or a nut therebelow to secure the baseI6 firmly on its seat.

It is preferred that, instead of placing the base I 6 directly on thechassis frame I I, a contact ring I9 be placed between the base I6 andthe chassis frame II. This contact ring is preferably made of a metalwhich is a fairly good and resilient conductor, such as phosphor bronzeor hard drawn copper. This will provide a low resistance con nectionbetween the base and the chassis frame at a plurality of points. At thesame time the base will provide a low resistance connector between thechassis frame and the shield I3 and thus ground the entire shield I3with very low resistance, effectively eliminating interference from theinterrupter within the shield.

It should be understood, of course, that any other apparatus besides theinterrupter could be located within the shield I3, although thestructure just disclosed has been designed with particular reference tothe interrupter on account of the severe shielding requirements which itpresents.

An inverted cup shield 26 is secured to the chassis frame beneath theshield I3 for housing some of the elements for the circuit of theinterrupter. A removable bottom or cover 32 is secured to the shield 26as shown in Fig. 1.

A metal shield 4| is shown in detail in Fig. 2 and illustrated in Fig. 1as assembled on the chassis II. Such a shield may desirably be used forany coils such as the intermediate frequency transformers as shown,which are each secured to the top of a shield by a nut and stud 42 asshown, the stud 42 being screwed through the insulating plate 44 onwhich the condensers are mounted, into the wooden post 55 on which thetransformer is mounted. The shield M is preferably a drawn tube formedof a non-magnetic material of low resistance, such as that knowncommercially as Eraydo. Shields of this type have been known heretoforeand have been secured in place by means of lugs riveted to the wall ofthe shield. The present invention avoids the expense of providing andattaching such separate lugs and the difficulty which they havesometimes caused because of being improperly attached. According to thepresent invention, straps or projections 4'! and 48 are stamped from thewall of the shield to positions offset from the plane of the wall of theshield in opposite directions as shown, thus forming a screw passageextending upwardly in the plane of the wall. The stamping die whichforms these straps is shaped to form threads on the surfaces of straps4i and 48 forming the screw passage. The shield M is then attached tothe chassis frame it by pointed screws 53, extending up through thechassis frame ll and screwed into the threads formed on the straps 41and 48, as illustrated in Fig. 1.

It will be understood that the vibrating interrupter I2 is used inconjunction with a power transformer and a power filter which must alsobe thoroughly shielded, both from the rest of the set and from eachother. A very effective and economical joint shield for this purpose isillustrated in Fig. l in which a shield 52 for the transformer issecured directly to the chassis frame I i and a shield 53 for the filteris secured on top of the transformer shield 52. The shield 52 may besecured in place by lugs 3 and screws The shield 53 is provided withdownwardly ex tending lugs 51' with which it may be secured to theshield 52, as by screws 58 threaded to the wall of the shield 52.

It is also desirable that the chassis as a whole be shielded by thecontainer. The container may comprise a box-like metallic structure 66having an open end into which the chassis is slid. For

' the sake of simplicity, one end of the container has been broken away.To properly position the chassis with respect to the container and totake the strain off of connecting plugs not shown, a sturdy tapered stud68 may be provided which may slip into a hole in a transverse member 69fixed within the casing as illustrated. According to common practice thecontainer 66 is grounded to the chassis frame. Also according toconventional practice, a removable cover H is provided for the open endof the container 66.

The proper grounding of this removable cover has long been a troublesomeproblem, bearing in mind the desirability that the grounding should beinexpensive and should not interfere with the removal or replacement ofthe cover. This problem has been solved by providing one or preferablyseveral spring contact strips 13 which are preferably spot welded to thetop of the cover and are provided with spring contact fingers (4 whichfirmly engage the inside of the casing 66 when the cover ll is pressedin place.

From the foregoing it is seen that there is provided a combination ofvarious structural features which make possible the manufacture of avery compact and thoroughly shielded receiving set for automobiles andthe like, at a relatively low expense, considering the quality of theset. Although of course many other features than those disclosed arenecessary for the complete set, it is not necessary to disclose suchfeatures since the features which are disclosed have general applicationand can be used with a wide variety of electrical devices and circuits.In other words, any suitable circuits and electrical equipment may beprovided for the structural features disclosed, in accordance with knownprinciples of radio design.

Although but one embodiment of my invention has been herein shown anddescribed, it is to be understood that the invention is not to belimited thereby, but is to be limited only by the scope of the appendedclaim.

I claim:

A walled metal shielding can open at the bottom for housing electricalapparatus on a radio receiver metal chassis with said can adapted forrigidly mounting on said receiver chassis in positive electrical andmechanical engagement therewith, said can having a screw-receiving holein each of at least two different walls thereof extending upwardly fromthe open bottom and each hole formed by structure in each of said wallscomprising a plurality of screw-engaging portions superimposed above oneanother in the respective can wall therefor and integral with therespective can wall, with said engaging portions in each respective canwall including one engaging portion extending in one direction away fromand out of the plane of that wall and the next superimposed engagingportion extending in the other direction away from and out of the planeof that wall, with said engaging portions in each of said respective canwalls each having screw threads on the inside face thereof to receive ascrew for mounting said shielding can on a radio receiver chassis.

DONALD H. MITCHELL.

